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Tumor R 2 * is a prognostic indicator of acute radiotherapeutic response in rodent tumors
Author(s) -
Rodrigues Loreta M.,
Howe Franklyn A.,
Griffiths John R.,
Robinson Simon P.
Publication year - 2004
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.20024
Subject(s) - carbogen , nuclear medicine , radiation therapy , medicine , oxygenation , radiology
Purpose To test the prognostic potential of tumor R 2 * with respect to radiotherapeutic outcome. Blood oxygenation level dependent (BOLD) MRI images are sensitive to changes in deoxyhemoglobin concentration through the transverse MRI relaxation rate R 2 * of tissue water, hence the quantitative measurement of tumor R 2 * may be related to tissue oxygenation. Methods and Materials Tumor growth inhibition in response to radiation was established for both GH3 prolactinomas and RIF‐1 fibrosarcomas with animals breathing either air or carbogen during radiation. In a separate cohort, the baseline R 2 * and carbogen (95% O 2 , 5% CO 2 )‐induced ΔR 2 * of rat GH3 prolactinomas and murine RIF‐1 fibrosarcomas were quantified using multigradient echo (MGRE) MRI prior to radiotherapy, and correlated with subsequent tumor growth inhibition in response to ionizing radiation, while the animals breathed air. Results A radiation dose of 15 Gy caused pronounced growth delay in both tumor models and transient regression of the GH3 prolactinomas. When the animals breathed carbogen during radiation, the growth delay/regression was enhanced only in the GH3 prolactinomas. The GH3 prolactinomas, which exhibit a relatively fast baseline R 2 * and large ΔR 2 * in response to carbogen breathing prior to radiotherapy, showed a substantial reduction in normalized tumor volume to 66 ± 3% with air breathing and 36 ± 5% with carbogen seven days after 15 Gy irradiation. In contrast, the effect of 15 Gy on the RIF‐1 fibrosarcomas, which give a relatively slow baseline R 2 * and negligible ΔR 2 * response to carbogen prior to treatment, showed a much smaller growth inhibition (143 ± 3% with air, 133 ± 12% with carbogen). Conclusion Quantitation of tumor R 2 * and carbogen‐induced ΔR 2 * by MGRE MRI provides completely noninvasive prognostic indicators of a potential acute radiotherapeutic response. J. Magn. Reson. Imaging 2004;19:482–488. © 2004 Wiley‐Liss, Inc.